Pixel, stage circuit and organic light emitting display device having the pixel and the stage circuit

ABSTRACT

A pixel includes a pixel circuit and an organic light emitting diode. The pixel circuit has first, second, third, and fourth transistors. The first transistor controls an amount of current flowing from a first driving power supply coupled to a first node to a second driving power supply through the organic light emitting diode. The turns on when a scan signal is supplied to a first scan line. The third transistor turns on when a scan signal is supplied to a second scan line. The fourth transistor turns on when a scan signal is supplied to a third scan line. The first transistor is a p-type Low Temperature Poly-Silicon thin film transistor and the third transistor and the fourth transistor are n-type oxide semiconductor thin film transistors.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2016-0083492, filed on Jul. 1, 2016,and entitled, “Pixel, Stage Circuit and Organic Light Emitting DisplayDevice Having the Pixel and the Stage Circuit,” is incorporated byreference herein in its entirety.

BACKGROUND 1. Field

One or more embodiments described herein relate to a pixel, a stagecircuit, and an organic light emitting display device including a pixeland a stage circuit.

2. Description of the Related Art

A variety of displays have been developed. Examples include liquidcrystal displays and organic light emitting displays. An organic lightemitting display generates an image based on light emitted from pixelsthat include organic light emitting diodes. Organic light emittingdisplays has advantages including high response speed and low powerconsumption.

An organic light emitting display includes pixels connected to datalines and scan lines. Each pixel uses a driving transistor to controlthe amount of current flowing from a first driving power supply, throughan organic light emitting diode, and to a second driving power supplybased on a data signal. The organic light emitting diode emits lightwith predetermined brightness based on the amount of current from thedriving transistor.

Attempts have been made to improve the performance of organic lightemitting displays. One approach involves setting the second drivingpower supply to a low voltage in an attempt to improve brightness.Another approach involves driving the display at low frequency in anattempt to reduce power consumption. However, both approaches may allowpredetermined current leakage to occur from a gate electrode of thedriving transistor. As a result, a data signal voltage for each pixelmay not be maintained during one frame period. Consequently, an imagewith a desired brightness may not be displayed.

SUMMARY

In accordance with one or more embodiments, a pixel comprising anorganic light emitting diode; a first transistor having a firstelectrode coupled to a first node and a second electrode coupled to ananode electrode of the organic light emitting diode, the firsttransistor to control an amount of current flowing from a first drivingpower supply coupled to the first node to a second driving power supplythrough the organic light emitting diode; a second transistor coupledbetween a data line and the first node, the second transistor to turn onwhen a scan signal is supplied to an ith first scan line, where i is anatural number; a third transistor coupled between a gate electrode andthe second electrode of the first transistor, the third transistor toturn on when a scan signal is supplied to an ith second scan line; afourth transistor coupled between the gate electrode of the firsttransistor and an initialization power supply, the fourth transistor toturn on when a scan signal is supplied to an ith third scan line,wherein the first transistor is a p-type Low Temperature Poly-Silicon(LTPS) thin film transistor and the third transistor and the fourthtransistor are n-type oxide semiconductor thin film transistors.

The second transistor may be a p-type LTPS thin film transistor. Thesecond transistor may be an n-type oxide semiconductor thin filmtransistor. The ith first scan line and the ith second scan line may bea same scan line. The pixel may include a fifth transistor coupledbetween the initialization power supply and the anode electrode of theorganic light emitting diode, the fifth transistor to turn on when thescan signal is supplied to the ith first scan line, the fifth transistoris a p-type LTPS thin film transistor.

The pixel may include a fifth transistor coupled between theinitialization power supply and the anode electrode of the organic lightemitting diode, the fifth transistor is to turn on when the scan signalis supplied to the ith second scan line, wherein the fifth transistor isan n-type oxide semiconductor thin film transistor.

The pixel may include a sixth transistor coupled between the secondelectrode of the first transistor and the anode electrode of the organiclight emitting diode, the sixth transistor is to turn off when a lightemission control signal is supplied to a light emission control line;and a seventh transistor coupled between the first node and the firstdriving power supply, the seventh transistor is to turn off when thelight emission control signal is supplied, wherein the sixth transistorand the seventh transistor are p-type LTPS thin film transistors.

In accordance with one or more other embodiments, a pixel includes anorganic light emitting diode; a first transistor to control an amount ofcurrent flowing from a first driving power supply coupled to a firstelectrode, through the organic light emitting diode, and to a seconddriving power supply based on a voltage of a first node; a secondtransistor coupled between the first node and a second electrode of thefirst transistor, the second transistor is to turn on when a scan signalis supplied to an ith first scan line; a storage capacitor coupledbetween the first node and a second node; a third transistor coupledbetween a data line and the second node, the third transistor to turn onwhen a scan signal is supplied to an ith second scan line; and a fourthtransistor coupled between the second node and an initialization powersupply, the fourth transistor to turn off when an inverted lightemission control signal is supplied to an inverted light emissioncontrol line, wherein the first transistor is a p-type LTPS thin filmtransistor and the third transistor and the fourth transistor are n-typeoxide semiconductor thin film transistors.

The second transistor may be a p-type LTPS thin film transistor. Thesecond transistor may be an n-type oxide semiconductor thin filmtransistor. The ith first scan line and the ith second scan line may bea same scan line. The pixel may include a fifth transistor coupledbetween the initialization power supply and an anode electrode of theorganic light emitting diode, the fifth transistor to turn on when thescan signal is supplied to the ith first scan line, the fifth transistoris a p-type LTPS thin film transistor.

The pixel may include a fifth transistor coupled between theinitialization power supply and an anode electrode of the organic lightemitting diode, the fifth transistor to turn on when the scan signal issupplied to the ith second scan line, wherein the fifth transistor is ann-type oxide semiconductor thin film transistor.

The pixel may include a sixth transistor coupled between the secondelectrode of the first transistor and the anode electrode of the organiclight emitting diode, the sixth transistor to turn off when a lightemission control signal is supplied to a light emission control line,wherein the sixth transistor is a p-type LIPS thin film transistor andthe light emission control signal and the inverted light emissioncontrol signal are inverted relative to each other.

In accordance with one or more other embodiments, a stage circuitincludes a first transistor, a second transistor, a third transistor,and a fourth transistor coupled in series between a first power supplyand a second power supply set to a voltage lower than the first powersupply; a fifth transistor, a sixth transistor, a seventh transistor,and an eighth transistor coupled in series between the first powersupply and the second power supply; and a ninth transistor and a tenthtransistor coupled in series between the first power supply and thesecond power supply, wherein: the first transistor is a p-type LIPS thinfilm transistor and has a gate electrode to receive an output signalfrom a previous stage or a start pulse the second transistor is a p-typeLIPS thin film transistor and has a gate electrode to receive a firstclock signal, the third transistor is an n-type oxide semiconductor thinfilm transistor and has a gate electrode to receive a second clocksignal having a same cycle as the first clock signal and an invertedphase, the fourth transistor is an n-type oxide semiconductor thin filmtransistor and has a gate electrode to receive the output signal fromthe previous stage and the start pulse, the fifth transistor is a p-typeLIPS thin film transistor and has a gate electrode coupled to an outputterminal, the sixth transistor is a p-type LIPS thin film transistor andhas a gate electrode to receive the second clock signal, the seventhtransistor is an n-type oxide semiconductor thin film transistor and hasa gate electrode to receive the first clock signal, the eighthtransistor is an n-type oxide semiconductor thin film transistor and hasa gate electrode coupled to the output terminal, the ninth transistor isa p-type LTPS thin film transistor and has a gate electrode coupled to afirst node, the tenth transistor is an n-type oxide semiconductor thinfilm transistor and has a gate electrode coupled to the first node, anda common node between the second transistor and the third transistor anda common node between the sixth transistor and the seventh transistorelectrically connected to the first node.

In accordance with one or more other embodiments, an organic lightemitting display device includes pixels connected to scan lines, lightemission control lines, and data lines; a scan driver to drive the scanlines and the light emission control lines; and a data driver to drivethe data lines, wherein at least one pixel in an ith horizontal line,among the pixels, includes: an organic light emitting diode; a firsttransistor having a first electrode coupled to a first node and a secondelectrode coupled to an anode electrode of the organic light emittingdiode, wherein the first transistor is to control an amount of currentflowing from a first driving power supply coupled to the first node,through the organic light emitting diode, and to a second driving powersupply; a second transistor coupled between a data line and the firstnode, the second transistor to turn on when a scan signal is supplied toan ith first scan line; a third transistor coupled between a gateelectrode and the second electrode of the first transistor, the thirdtransistor to turn on when a scan signal is supplied to an ith secondscan line; and a fourth transistor coupled between the gate electrode ofthe first transistor and an initialization power supply, the fourthtransistor to turn on when a scan signal is supplied to an ith thirdscan line, wherein the first transistor is a p-type LTPS thin filmtransistor and the third transistor and the fourth transistor are n-typeoxide semiconductor thin film transistors.

The pixel may include a fifth transistor coupled between theinitialization power supply and the anode electrode of the organic lightemitting diode, the fifth transistor to turn on when the scan signal issupplied to the ith second scan line, wherein the fifth transistor is ann-type oxide semiconductor thin film transistor. The pixel may includesixth transistor coupled between the second electrode of the firsttransistor and the anode electrode of the organic light emitting diode,the sixth transistor to turn off when a light emission control signal issupplied to an ith light emission control line; and a seventh transistorcoupled between the first node and the first driving power supply, theseventh transistor to turn off when the light emission control signal issupplied, wherein the sixth transistor and the seventh transistor arep-type LTPS thin film transistors.

The scan driver may include a plurality of stage circuits to drive thescan lines and the light emission control lines, and at least one of thestage circuits may include an eleventh transistor, a twelfth transistor,a thirteenth transistor, and a fourteenth transistor coupled in seriesbetween a first power supply and a second power supply set to a voltagelower than the first power supply; a fifteenth transistor, a sixteenthtransistor, a seventeenth transistor and an eighteenth transistorcoupled in series between the first power supply and the second powersupply; and a nineteenth transistor and a twentieth transistor coupledin series between the first power supply and the second power supply,wherein the eleventh transistor is a p-type LTPS thin film transistorand has a gate electrode to receive an output signal from a previousstage or a start pulse, the twelfth transistor is set to a p type LIPSthin film transistor and has a gate electrode to receive a first clocksignal, the thirteenth transistor is an n-type oxide semiconductor thinfilm transistor and has a gate electrode to receive a second clocksignal having a same cycle as the first clock signal and an invertedphase, the fourteenth transistor is an n-type oxide semiconductor thinfilm transistor and has a gate electrode to receive the output signalfrom the previous stage or the start pulse, the fifteenth transistor isset to a p type LTPS thin film transistor and has a gate electrodecoupled to an output terminal, the sixteenth transistor is a p-type LTPSthin film transistor and has a gate electrode to receive the secondclock signal, the seventeenth transistor is an n-type oxidesemiconductor thin film transistor and has a gate electrode to receivethe first clock signal, the eighteenth transistor is an n type oxidesemiconductor thin film transistor and has a gate electrode coupled tothe output terminal; the nineteenth transistor is a p-type LTPS thinfilm transistor and has a gate electrode coupled to the first node, thetwentieth transistor is an n-type oxide semiconductor thin filmtransistor and has a gate electrode coupled to the first node, and acommon node between the twelfth transistor and the thirteenth transistorand a common node between the sixteenth transistor and the seventeenthtransistor are electrically connected to the first node.

In accordance with one or more other embodiments, a pixel includes afirst transistor to control current to a light emitter; and a secondtransistor coupled to at least one of the light emitter, the firsttransistor, or a capacitor, wherein the first transistor is a LowTemperature Poly-Silicon (LTPS) transistor and the second transistor isdifferent from an LIPS transistor, the first and second transistorshaving different conductivity types. The second transistor may be anoxide semiconductor transistor. The first transistor may be a p-typetransistor and the second transistor may be an n-type transistor. Thesecond transistor may place the first transistor in a diode-connectedstate when turned on. The second transistor may be connected to a dataline.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1 illustrates an embodiment of an organic light emitting displaydevice;

FIG. 2 illustrates an embodiment of a pixel;

FIGS. 3A-3B illustrate waveforms for embodiments of a method for drivinga pixel;

FIG. 4 illustrates another embodiment of a pixel;

FIG. 5 illustrates another embodiment of a pixel;

FIG. 6 illustrates an embodiment of a method of driving the pixel inFIG. 5;

FIG. 7 illustrates another embodiment of a pixel;

FIG. 8 illustrates a waveform for an embodiment of a method for drivinga pixel;

FIG. 9 illustrates another embodiment of a pixel;

FIG. 10 illustrates a waveform for an embodiment of a method for drivinga pixel; and

FIG. 11 illustrates an embodiment of a stage circuit.

DETAILED DESCRIPTION

Example embodiments will now be described with reference to thedrawings; however, they may be embodied in different forms and shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey exemplary implementations to thoseskilled in the art. The embodiments (or portions thereof) may becombined to form additional embodiments.

In the drawings, the dimensions of layers and regions may be exaggeratedfor clarity of illustration. It will also be understood that when alayer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it canbe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it canbe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

It will be understood that when an element is referred to as being“connected to” another element, it can be directly connected to theelement or it can be electrically connected to the element with one ormore intervening elements interposed. In addition, in the drawings,parts that are not related to the present invention are omitted in orderto clarify the present invention. Like reference numerals refer to likeelements throughout.

FIG. 1 illustrates an embodiment of an organic light emitting displaydevice which includes pixels 140 connected to scan lines S11 to S1 n,S21 to S2 n and S31 to S3 n, light emission control lines E1 to En, anddata lines D1 to Dm, a scan driver 110 driving the scan lines S11 to S1n, S21 to S2 n and S31 to S3 n and the light emission control lines E1to En, a data driver 120 driving the data lines D1 to Dm, and a timingcontroller 150 controlling the scan driver 110 and the data driver 120.

The timing controller 150 may generate a data driving control signal DCSand a scan driving control signal SCS based on externally suppliedsynchronous signals. The data driving control signal DCS and the scandriving control signal SCS generated by the timing controller 150 may besupplied to the data driver 120 and the scan driver 110, respectively.In addition, the timing controller 150 may realign and supply externallysupplied data to the data driver 120.

The scan driving control signal SCS may include start pulses and clocksignals. The start pulses may be applied to control the first timings ofscan signals and light emission control signals. The clock signals maybe applied to shift the start pulses.

The data driving control signal DCS may include a source start pulse andclock signals. The source start pulse may be applied to control asampling start point of data and the clock signals may be applied tocontrol a sampling operation.

The scan driver 110 may receive the scan driving control signal SCS fromthe timing controller 150. The scan driver 110 receiving the scandriving control signal SCS may supply scan signals to the first scanlines S11 to S1 n, the second scan lines S21 to S2 n, and the third scanlines S31 to S3 n. For example, the scan driver 110 may sequentiallysupply first scan signals to the first scan lines S11 to S1 n,sequentially supply second scan signals to the second scan lines S21 toS2 n, and sequentially supply third scan signals to the third scan linesS31 to S3 n. When the first, second and third scan signals aresequentially supplied, pixels 140 may be selected in units of horizontallines.

The scan driver 110 may supply a second scan signal to an ith secondscan line S21 to overlap a first scan signal supplied to an ith firstscan line S1 i, where i is a natural number. The first scan signal andthe second scan signal may be set to signals having opposite polarities.For example, the first scan signal may be set to a low voltage and thesecond scan signal may be set to a high voltage. In addition, the scandriver 110 may supply a third scan signal to an ith third scan line S3 ibefore supplying the second scan signal to the ith second scan line S2i. The third scan signal may be set to a high voltage. In addition, theith third scan line scan line S3 i may be replaced by an (i−1)th secondscan line S2 i-1.

In addition, each of the first, second, and third scan signals may beset to a gate-on voltage. Transistors in the pixel 140 may be set to aturn-on state based on the first scan signal. Another transistor in thepixel 140 may be set to a turn-on state based on the second signal.Another transistor in the pixel 140 may be set to a turn-on state basedon the third scan signal.

The scan driver 110 receiving the scan driving control signal SCS maysupply light emission control signals to the light emission controllines E1 to En. For example, the scan driver 110 may sequentially supplythe light emission control signals to the light emission control linesE1 to En. Each of the light emission control signals may be applied tocontrol emission time of each of the pixels 140. Thus, in oneembodiment, a light emission control signal may be set to have a greaterwidth than a scan signal. For example, the scan driver 110 may supplyscan signals to an (i−1)th first scan line S1 i-1 and the ith first scanline S1 i to overlap with the light emission control signal supplied toan ith light emission control signal Ei.

The scan driver 110 may be mounted on a substrate, for example, througha thin film process. In one embodiment, the scan driver 110 may belocated at different sides of the pixel unit 130. In addition, scandriver 110 is illustrated to supply the scan signals and light emissioncontrol signals. In another embodiment, different drivers may supply thescan signals and light emission control signals.

The light emission control signals may be set to gate-off voltages(e.g., high voltages) to turn off transistors in the pixels 140.Transistors in the pixel 140 may be turned off based on the lightemission control signal and may be turned on for another period or theremaining period.

The data driver 120 may supply data signals to the data lines D1 to Dmbased on the data driving control signal DCS. The data signals suppliedto the data lines D1 to Dm may be supplied to the pixels 140 selected bythe first scan signals (or second scan signals). The data driver 120 maysupply the data signals to the data lines D1 to Dm in synchronizationwith the first scan signals (or second scan signals). The data driver120 may supply the data signals to the data lines D1 to Dm insynchronization with the first scan signals (or second scan signals).

The pixel unit 130 may include the pixels 140 coupled to the S11 to S1n, S21 to S2 n, and S31 to S3 n, the light emission control lines E1 toEn, and the data lines D1 to Dm. The pixels 140 may receive a firstdriving power supply ELVDD, a second driving power supply ELVSS, and aninitialization power supply Vint from an external device.

Each of the pixels 140 may include a driving transistor and an organiclight emitting diode. The driving transistor may control the amount ofcurrent flowing from the first driving power supply ELVDD, through theorganic light emitting diode, and to the second driving power supplyELVSS based on a data signal. A gate electrode of the driving transistormay be initialized based on a voltage of the initialization power supplyVint before the data signal is supplied.

In FIG. 1, n scan lines S11 to S1 n, n scan lines S21 to S2 n, n scanlines S31 to S3 n, and n light emission control lines E1 to En areillustrated. In another embodiment, based on the circuit configurationof the pixels 140, pixels in the current horizontal line may beadditionally connected to a scan line in the previous horizontal line.In this circuit configuration of the pixels 140, dummy scan lines and/ordummy light emission control lines may be additionally formed.

In FIG. 1, the first scan lines S11 to S1 n, the second scan lines S21to S2 n, and the third scan lines S31 to S3 n. In another embodiment,only one of the first, second, and third scan lines S11 to S1 n, S21 toS2 n, and S31 to S3 n may be included based on the circuit configurationof the pixels 140.

In FIG. 1, light emission control lines E1 to En are illustrated. Inanother embodiment, inverted light emission control lines may further beincluded based on the circuit configuration of the pixels 140. Theinverted light emission control lines may receive inverted lightemission control signals of the light emission control signals.

FIG. 2 illustrates an embodiment of a pixel, which, for example, may berepresentative of pixels 140. For convenience of explanation, the pixelis illustrated as being located in an ith horizontal line and connectedto an mth data line Dm.

Referring to FIG. 2, the pixel 140 may include an oxide semiconductorthin film transistor and a Low Temperature Poly-Silicon (LTPS) thin filmtransistor. The oxide semiconductor thin film transistor may include agate electrode, a source electrode, and a drain electrode. The oxidesemiconductor thin film transistor may include an active layer includingan oxide semiconductor material. The oxide semiconductor material maybe, for example, an amorphous or crystalline oxide semiconductormaterial. The oxide semiconductor thin film transistor may be, forexample, an n-type transistor.

The LTPS thin film transistor may include a gate electrode, a sourceelectrode, and a drain electrode. The LTPS thin film transistor mayinclude an active layer including polysilicon. The LTPS thin filmtransistor may be, for example, a p-type thin film transistor or an ntype thin film transistor. The LTPS thin film transistor may have highelectron mobility and high driving characteristics.

The oxide semiconductor thin film transistor may allow for a lowtemperature process and have lower charge mobility than the LTPS thinfilm transistor. The oxide semiconductor thin film transistor may haveexcellent off current characteristics.

The pixel 140 may include a pixel circuit 142 and an organic lightemitting diode OLED. The organic light emitting diode OLED may have ananode electrode coupled to the pixel circuit 142 and a cathode electrodecoupled to the second driving power supply ELVSS. The organic lightemitting diode OLED may emit light with a predetermined brightness basedon the amount of current from the pixel circuit 142.

The pixel circuit 142 may control the amount of current flowing from thefirst driving power supply ELVDD, through the organic light emittingdiode OLED, and to the second driving power supply ELVSS based on a datasignal. The pixel circuit 142 may include a first transistor M1(L)(driving transistor), a second transistor M2(L), a third transistorM3(O), a fourth transistor M4(O), a fifth transistor M5(L), a sixthtransistor M6(L), a seventh transistor M7(L), and a storage capacitorCst.

The first transistor M1(L) may have a first electrode coupled to a firstnode N1, a second electrode coupled to a first electrode of the sixthtransistor M6(L), and a gate electrode coupled to a second node N2. Thefirst transistor M1(L) may control the amount of current supplied fromthe first driving power supply ELVDD, through the organic light emittingdiode OLED, and to the second driving power supply ELVSS based on avoltage stored in the storage capacitor Cst. To ensure a high drivingspeed, the first transistor M1(L) may include an LTPS thin filmtransistor and, for example, may be a p-type transistor.

The second transistor M2(L) may be coupled between the data line Dm andthe first node N1. A gate electrode of the second transistor M2(L) maybe coupled to the ith first scan line S1 i. The second transistor M2(L)may be turned on when the first scan signal is supplied to the ith firstscan line S1 i to electrically connect the data line Dm to the firstnode N1. The second transistor M2(L) may include an LTPS thin filmtransistor and, for example, may be a p-type transistor.

The third transistor M3(O) may be coupled between a second electrode ofthe first transistor M1(L) and the second node N2. A gate electrode ofthe third transistor M3(O) may be coupled to the ith second scan line S2i. The third transistor M3(O) may be turned on when a second scan signalis supplied to the ith second scan line S2 i, in order to place thefirst transistor M1(L) in a diode-connected state.

When the third transistor M3(O) includes an oxide semiconductor thinfilm transistor, the third transistor M3(O) may be, for example, ann-type transistor. When the third transistor M3(O) is an oxidesemiconductor thin film transistor, leakage current flowing from thesecond node N2 to the second electrode of the first transistor M1(L) maybe reduced, so that an image with desired brightness may be displayed.

The fourth transistor M4(O) may be connected between the second node N2and the initialization power supply Vint. A gate electrode of the fourthtransistor M4(O) may be coupled to an ith third scan line S3 i. Thefourth transistor M4(O) may be turned on when a third scan signal issupplied to the ith third scan line S3 i, in order to supply a voltageof the initialization power supply Vint to the second node N2.

The fourth transistor M4(O) may be an oxide semiconductor thin filmtransistor and, for example, may be an n-type transistor. When thefourth transistor M4(O) is an oxide semiconductor thin film transistor,leakage current flowing from the second node N2 to the initializationpower supply Vint may be reduced in order to display an image withdesired brightness.

The fifth transistor M5(L) may be connected between the anode electrodeof the organic light emitting diode OLED and the initialization powersupply Vint. The gate electrode of the fifth transistor M5(L) may becoupled to the ith first scan line S1 i. The fifth transistor M5(L) maybe turned on when the first scan signal is supplied to the ith firstscan line S1 i, in order to supply the voltage of the initializationpower supply Vint to the anode electrode of the organic light emittingdiode OLED. The fifth transistor M5(L) may be an LTPS thin filmtransistor and, for example, may be a p-type transistor.

The voltage of the initialization power supply Vint may be lower thanthe range of data voltages for the data signals. When the voltage of theinitialization power supply Vint is supplied to the anode electrode ofthe organic light emitting diode OLED, a parasitic capacitor (e.g.,organic capacitor Coled) of the organic light emitting diode OLED may bedischarged. When the organic capacitor Coled is discharged, blackexpression capabilities of the pixel 140 may be improved.

In one embodiment, the organic capacitor Coled may store a predeterminedvoltage based on current from the pixel circuit 142 during the previousframe. When the predetermined voltage is stored in the organic capacitorColed, the organic light emitting diode OLED may easily emit light atlow current.

A black data signal may be supplied to the pixel circuit 142 during thecurrent frame period. When the black data signal is supplied, the pixelcircuit 142 may not, ideally, supply current to the organic lightemitting diode OLED. However, even when the black data signal issupplied, predetermined leakage current may be supplied from the firsttransistor M1(L) to the organic light emitting diode OLED. When theorganic capacitor Coled stores the predetermined voltage, the organiclight emitting diode OLED may finely emit light and, thus, blackexpression capabilities may be deteriorated.

According to one embodiment, when the organic capacitor Coled isdischarged by the initialization power supply Vint, the organic lightemitting diode OLED may be set to a non-light emitting state even whenleakage current is supplied from the first transistor M1(L). Thus, theleakage current from the first transistor M1(L) may previously chargethe organic capacitor Coled, so that the organic capacitor Coled maymaintain a non-light emitting state.

The sixth transistor M6(L) may be coupled between the second electrodeof the first transistor M1(L) and the anode electrode of the organiclight emitting diode OLED. In addition, a gate electrode of the sixthtransistor M6(L) may be coupled to a light emission control line Ei. Thesixth transistor M6(L) may be turned off when a light emission controlsignal is supplied to the light emission control line Ei and may beturned on when the light emission control signal is not supplied. Thesixth transistor M6(L) may be an LTPS thin film transistor and, forexample, may be a p-type transistor.

The seventh transistor M7(L) may be coupled between the first drivingpower supply ELVDD and the first node N1. A gate electrode of theseventh transistor M7(L) may be connected to the light emission controlline Ei. The seventh transistor M7(L) may be turned off when a lightemission control signal is supplied to the light emission control lineEi, and may be turned on when the light emission control signal is notsupplied. The seventh transistor M7(L) may be an LTPS thin filmtransistor and, for example, may be a p-type transistor.

The storage capacitor Cst may be coupled between the first driving powersupply ELVDD and the second node N2. The storage capacitor Cst may storea voltage corresponding to the data signal and a threshold voltage ofthe first transistor M1(L).

In the present embodiment, the third transistor M3(O) and the fourthtransistor M4(O) coupled to the second node N2 may be oxidesemiconductor thin film transistors. When the third transistor M3(O) andthe fourth transistor M4(O) are oxide semiconductor thin filmtransistors, current leakage from the second node N2 may be reduced. Asa result, an image with desired brightness may be displayed.

In the present embodiment, transistors M7(L), M1(L), and M6(L) in acurrent supply path for supplying current to the organic light emittingdiode OLED may be LTPS thin film transistors. When transistors M7(L),M1(L), and M6(L) in the current supply path are LTPS thin filmtransistors, current may be stably supplied to the organic lightemitting diode OLED by high driving characteristics.

FIG. 3A illustrates a waveform corresponding to an embodiment of amethod for driving a pixel, for example, as illustrated in FIG. 2.Referring to FIG. 3A, a light emission control signal (high voltage) maybe supplied to the light emission control line Ei to turn off the sixthtransistor M6(L) and the seventh transistor M7(L), which are p-typetransistors. When the sixth transistor M6(L) is turned off, electricalconnection between the first transistor M1(L) and the organic lightemitting diode OLED may be blocked. When the seventh transistor M7(L) isturned off, electrical connection between the first driving power supplyELVDD and the first node N1 may be blocked. Therefore, during a periodin which the light emission control signal is supplied to the lightemission control line Ei, the pixel 140 may be set to a non-lightemitting state.

Subsequently, a third scan signal (high voltage) may be supplied to anith third scan line S3 i. When the third scan signal is supplied to theith third scan line S3 i, the fourth transistor M4(O), which is ann-type transistor, may be turned on. When the fourth transistor M4(O) isturned on, the voltage of the initialization power supply Vint may besupplied to the second node N2.

After the voltage of the initialization power supply Vint is supplied tothe second node N2, a first scan signal (low voltage) may be supplied tothe ith first scan line S1 i and a second scan signal (high voltage) maybe supplied to the ith second scan line S2 i.

When the first scan signal is supplied to the ith first scan line S1 i,the second transistor M2(L) and the fifth transistor M5(L), which arep-type transistors, may be turned on. When the fifth transistor M5(L) isturned on, the voltage of the initialization power supply Vint may besupplied to the anode electrode of the organic light emitting diodeOLED. When the voltage of the initialization power supply Vint issupplied to the anode electrode of the organic light emitting diodeOLED, the organic capacitor Coled may be discharged. When the secondtransistor M2(L) is turned on, the data line Dm and the first node N1may be electrically connected to each other to supply the data signalfrom the data line Dm to the first node N1.

When the second scan signal is supplied to the ith second scan line S2i, the third transistor M3(O), which is an n-type transistor, may beturned on. When the third transistor M3(0) is turned on, the firsttransistor M1(L) may be placed in a diode-connected state. Since secondnode N2 is initialized to the voltage of initialization power supplyVint lower than the data signal, the first transistor M1(L) may beturned on.

When the first transistor M1(L) is turned on, the data signal suppliedto the first node N1 may pass to the second node N2 through the firsttransistor M1(L) in a diode-connected state. The second node N2 may beset to a voltage corresponding to the data signal and the thresholdvoltage of the first transistor M1(L). The storage capacitor Cst maystore the voltage applied to the second node N2.

After the voltage of the second node N2 is stored in the storagecapacitor Cst, supply of the light emission control signal to the lightemission control line Ei may be stopped. When the supply of the lightemission control signal to the light emission control line Ei isstopped, the sixth transistor M6(L) and the seventh transistor M7(L) maybe turned on.

When the sixth transistor M6(L) is turned on, the first transistor M1(L)may be electrically connected to the organic light emitting diode OLED.When the seventh transistor M7(L) is turned on, the first driving powersupply ELVDD may be electrically connected to the first node N1. Thefirst transistor M1(L) may control the amount of current flowing fromthe first driving power supply ELVDD through the organic light emittingdiode OLED to the second driving power supply ELVSS based on the voltageof the second node N2.

The second node N2 may be connected to the third transistor M3(O) andthe fourth transistor M4(O), which are oxide semiconductor thin filmtransistors, to reduce leakage current. Therefore, the second node N2may maintain a desired voltage during one frame period, and the pixel140 may generate light with desired brightness based on a data signalduring one frame period.

According to an embodiment, the ith third scan line S3 i may be replacedby the (i−1)th second scan line S2 i-1. In this embodiment, asillustrated in FIG. 3B, a second scan signal supplied to the (i−1)thsecond scan line S2 i-1 may be supplied to the fourth transistor M4(O).Otherwise, the same operations described above may be performed.

FIG. 4 illustrates another embodiment of a pixel 140 a, which, forexample, may be representative of the pixels in the display device ofFIG. 1. Referring to FIG. 4, the pixel 140 a may include a pixel circuit142′ and the organic light emitting diode OLED.

The organic light emitting diode OLED has an anode electrode coupled tothe pixel circuit 142′ and a cathode electrode coupled to the seconddriving power supply ELVSS. The organic light emitting diode OLED maygenerate light with predetermined brightness based on the amount ofcurrent supplied from the pixel circuit 142′.

The pixel circuit 142′ may include the first transistor M1(L), thesecond transistor M2(L), the third transistor M3(0), the fourthtransistor M4(0), the fifth transistor M5(0), the sixth transistorM6(L), the seventh transistor M7(L) and the storage capacitor Cst. Thepixel circuit 142′ in FIG. 4 may have substantially the sameconfiguration as the pixel circuit 142 in FIG. 2, except that the fifthtransistor M5(O) is an oxide semiconductor thin film transistor.

The fifth transistor M5(O) may be coupled between the anode electrode ofthe organic light emitting diode OLED and the initialization powersupply Vint. The gate electrode of the fifth transistor M5(O) may becoupled to the ith second scan line S2 i. The fifth transistor M5(O) maybe turned on when a second scan signal is supplied to the ith secondscan line S2 i, in order to supply a voltage of the initialization powersupply Vint to the anode electrode of the organic light emitting diodeOLED. The fifth transistor M5(O) may be an n-type transistor.

When the fifth transistor M5(O) is an oxide thin film transistor,leakage current supplied to the initialization power supply Vint fromthe anode electrode of the organic light emitting diode OLED may bereduced during light emission time. When the leakage current suppliedfrom the anode electrode of the organic light emitting diode OLED to theinitialization power supply Vint is reduced, the organic light emittingdiode OLED may generate light with desired brightness.

In addition, the fifth transistor M5(O) may be turned on when the secondscan signal is supplied to the ith second scan line S2 i. In oneembodiment, the fifth transistor M5(O) may perform substantially thesame operations as described in FIG. 2.

FIG. 5 illustrates another embodiment of a pixel 140 b which includes apixel circuit 142″ and the organic light emitting diode OLED. Referringto FIG. 5, the pixel 140 b may include a pixel circuit 142″ and theorganic light emitting diode OLED.

The organic light emitting diode OLED has an anode electrode which maybe coupled to the pixel circuit 142″ and a cathode electrode coupled tothe second driving power supply ELVSS. The organic light emitting diodeOLED may generate light with desired brightness based on the amount ofcurrent supplied from the pixel circuit 142″.

The pixel circuit 142″ may include the first transistor M1(L), a secondtransistor M2(O), the third transistor M3(O), the fourth transistorM4(O), the fifth transistor M5(0), the sixth transistor M6(L), theseventh transistor M7(L) and the storage capacitor Cst. The pixelcircuit 142″ may have substantially the same configuration as the pixelcircuit 142′ in FIG. 4, except that the second transistor M2(O) is anoxide semiconductor thin film transistor.

The second transistor M2(O) may be coupled between the data line Din andthe first node N1. A gate electrode of the second transistor M2(O) maybe coupled to the ith second scan line S2 i. The second transistor M2(O)may be turned on when the second scan signal is supplied to the ithsecond scan line S2 i to electrically connect the data line Dm to thefirst node N1. The second transistor M2(O) may be an n-type transistor.

When the second transistor M2(O) is an oxide thin film transistor,undesirable current flow between the first node N1 and the data line Dmmay be reduced and the organic light emitting diode OLED may generatelight with desired brightness. In addition, when the second transistorM2(O) is an n-type transistor, a first scan line S1 may be removed.

FIG. 6 illustrates a waveform of an embodiment of a method for drivingthe pixel 140 b in FIG. 5. Referring to FIG. 6, a light emission controlsignal may be supplied to the light emission control line Ei to turn offthe sixth transistor M6(L) and the seventh transistor M7(L). When thesixth transistor M6(L) and the seventh transistor M7(L) are turned off,the pixel 140 may be set to a non-light emitting state.

Subsequently, a third scan signal may be supplied to the ith third scanline S3 i. When the third scan signal is supplied to the ith third scanline S3 i, the fourth transistor M4(O) may be turned on. When the fourthtransistor M4(O) is turned on, the voltage of the initialization powersupply Vint may be supplied to the second node N2.

A second scan signal may be supplied to the ith second scan line S2 iafter the voltage of the initialization power supply Vint is supplied tothe second node N2. When the second scan signal is supplied to the ithsecond scan line S2 i, the second transistor M2(O), the third transistorM3(O), and the fifth transistor M5(O) are turned on. When the fifthtransistor M5(O) is turned on, the voltage of the initialization powersupply Vint may be supplied to the anode electrode of the organic lightemitting diode OLED.

When the second transistor M2(O) is turned on, the data line Dm may beelectrically connected to the first node N1 to supply a data signal fromthe data line Dm to the first node N1.

When the third transistor M3(O) is turned on, the first transistor M1(L)may be placed in a diode-connected state. Since the second node N2 isinitialized to the voltage of the initialization power supply Vint lowerthan the data signal, the first transistor M1(L) may be turned on. Whenthe first transistor M1(L) is turned on, the data signal supplied to thefirst node N1 may pass to the second node N2 through the firsttransistor M1(L) in a diode-connected state. The second node N2 may beset to a voltage corresponding to the data signal and a thresholdvoltage of the first transistor M1(L). The storage capacitor Cst maystore a voltage applied to the second node N2.

After the voltage of the second node N2 is stored in the storagecapacitor Cst, supply of the light emission control signal to the lightemission control line Ei may be stopped. The sixth transistor M6(L) andthe seventh transistor M7(L) may be turned on when the supply of thelight emission control signal to the light emission control line Ei isstopped.

When the sixth transistor M6(L) and the seventh transistor M7(L) areturned on, a current supply path may be formed from the first drivingpower supply ELVDD, through the organic light emitting diode OLED, andto the second driving power supply ELVSS. The first transistor M1(L) maycontrol the amount of current flowing from the first driving powersupply ELVDD through the organic light emitting diode OLED to the seconddriving power supply ELVSS based on the voltage of the second node N2.

According to the present embodiment, transistors M7(L), M1(L), and M6(L)in the current supply path for supplying current to the organic lightemitting diode OLED may be LIPS thin film transistors. When transistorsM7(L), M1(L), and M6(L) in the current supply path are LIPS thin filmtransistors, current may be stably supplied to the organic lightemitting diode OLED by high driving characteristics.

In addition, according to the present embodiment, the transistors M2(O),M3(O), M4(O), and M5(O) which are not in the current supply path may beoxide semiconductor thin film transistors. When the transistors M2(O),M3(O), M4(O), and M5(O) which are not in the current supply path areoxide semiconductor thin film transistors, leakage current may bereduced and an image with desired brightness may be displayed.

FIG. 7 illustrates another embodiment of a pixel 140 c, which, forexample, may be presentative of the pixels in the display device ofFIG. 1. For convenience of explanation, in FIG. 7, pixel 140 c isillustrated as being located in the ith horizontal line and the mth dataline Dm.

Referring to FIG. 7, the pixel 140 c may include a pixel circuit 144 andorganic light emitting diode OLED. The organic light emitting diode OLEDhas an anode electrode coupled to the pixel circuit 144 and a cathodeelectrode coupled to the second driving power supply ELVSS. The organiclight emitting diode OLED may emit light with predetermined brightnessbased on the amount of current from the pixel circuit 144.

The pixel circuit 144 may control the amount of current flowing from thefirst driving power supply ELVDD, through the organic light emittingdiode OLED, and to the second driving power supply ELVSS based on a datasignal. The pixel circuit 144 may include a first transistor M11(L), asecond transistor M12(L), a third transistor M13(O), a fourth transistorM14(O), a fifth transistor M15(L), a sixth transistor M16(L) and thestorage capacitor Cst.

The first transistor M11(L) has a first electrode coupled to the firstdriving power supply ELVDD, a second electrode coupled to a firstelectrode of the sixth transistor M16(L), and a gate electrode coupledto the first node N1. The first transistor M11(L) may control the amountof current flowing from the first driving power supply ELVDD, throughthe organic light emitting diode OLED, and to the second driving powersupply ELVSS based on a voltage of the first node N1. To ensure highdriving speed, first transistor M11(L) may be, for example, a p-typeLTPS thin film transistor.

The second transistor M12(L) may be coupled between the first node N1and a second electrode of the first transistor M11(L). A gate electrodeof the second transistor M12(L) may be coupled to the ith first scanline S1 i. The second transistor M12(L) may be turned on when a firstscan signal is supplied to the ith first scan line S1 i. When the secondtransistor M12(L) is turned on, the first transistor M11(L) may beplaced in a diode-connected state. The second transistor M12(L) may be,for example, a p-type LTPS thin film transistor.

The third transistor M13(O) may be coupled between the data line Dm andthe second node N2. A gate electrode of the third transistor M13(O) maybe coupled to the ith second scan line S2 i. The third transistor M13(O)may be turned on when a second scan signal is supplied to the ith secondscan line S2 i. When the third transistor M13(O) is turned on, the dataline Dm may be electrically connected to the second node N2.

When the third transistor M13(O) is an oxide semiconductor thin filmtransistor, the third transistor M13(O) may be, for example, an n-typetransistor. When the third transistor M13(O) is an oxide semiconductorthin film transistor, leakage current between the second node N2 and thedata line Dm may be reduced and an image with desired brightness may bedisplayed.

The fourth transistor M14(O) may be coupled between the second node N2and the initialization power supply Vint. A gate electrode of the fourthtransistor M14(O) may be coupled to an inverted light emission controlline /Ei. The fourth transistor M14(O) may be turned off when aninverted light emission control signal is supplied to the inverted lightemission control line /Ei, and may be turned on when the inverted lightemission control signal is not supplied. When the fourth transistorM14(O) is turned on, a voltage of the initialization power supply Vintmay be supplied to the second node N2.

When the fourth transistor M14(O) is an oxide semiconductor thin filmtransistor, the fourth transistor M14(O) may be, for example, an n-typetransistor. When the fourth transistor M14(O) is an oxide semiconductorthin film transistor, leakage current between the second node N2 and theinitialization power supply Vint may be reduced and an image withdesired brightness may be displayed.

In one embodiment, the inverted light emission control signal suppliedto the inverted light emission control line /Ei may be set to aninverted signal of the light emission control signal supplied to thelight emission control line Ei. For example, when the light emissioncontrol signal is set to a predetermined high voltage, the invertedlight emission control signal may be set to a predetermined low voltage.

The fifth transistor M15(L) may be coupled between the anode electrodeof the organic light emitting diode OLED and the initialization powersupply Vint. A gate electrode of the fifth transistor M15(L) may becoupled to the ith first scan line S1 i. The fifth transistor M15(L) maybe turned on when the first scan signal is supplied to the ith firstscan line S1 i. When the fifth transistor M15(L) is turned on, thevoltage of the initialization power supply Vint may be supplied to theanode electrode of the organic light emitting diode OLED. The fifthtransistor M15(L) may be, for example, a p-type LTPS thin filmtransistor.

The sixth transistor M16(L) may be coupled between a second electrode ofthe first transistor M11(L) and the anode electrode of the organic lightemitting diode OLED. A gate electrode of the sixth transistor M16(L) maybe coupled to the light emission control line Ei. The sixth transistorM16(L) may be turned off when the light emission control signal issupplied to the light emission control line Ei, and may be turned onwhen the light emission control signal is not supplied. The sixthtransistor M16(L) may be, for example, a p-type LTPS thin filmtransistor.

The storage capacitor Cst may be coupled between the first node N1 andthe second node N2. The storage capacitor Cst may store a voltagecorresponding to the data signal and a threshold voltage of the firsttransistor M11(L).

According to the present embodiment, the third transistor M13(O) and thefourth transistor M14(O) coupled to the second node N2 may be oxidesemiconductor thin film transistors. When the third transistor M13(O)and the fourth transistor M14(O) are oxide semiconductor thin filmtransistors, voltage variations of the second node N2 by leakage currentmay be reduced and an image with desired brightness may be displayed.

According to the present embodiment, transistors M11(L) and M16(L) inthe current supply path for supplying current to the organic lightemitting diode OLED may be LIPS thin film transistors. When transistorsM11(L) and M16(L) in the current supply path are LIPS thin filmtransistors, current may be stably supplied to the organic lightemitting diode OLED by high driving characteristics.

FIG. 8 illustrates an embodiment of a waveform for the pixel in FIG. 7.In FIG. 8, a first scan signal may be supplied to the first scan line S1i and a second scan signal may be supplied to the second scan line S2 i.

When the first scan signal is supplied to the first scan line S1 i, thesecond transistor M12(L) and the fifth transistor M15(L) may be turnedon. When the fifth transistor M15(L) is turned on, a voltage of theinitialization power supply Vint may be supplied to the anode electrodeof the organic light emitting diode OLED. When the voltage of theinitialization power supply Vint is supplied to the anode electrode ofthe organic light emitting diode OLED, the organic capacitor Coled maybe discharged.

When the second transistor M12(L) is turned on, the first transistorM11(L) may be placed in a diode-connected state. The first node N1 maybe electrically connected to the initialization power supply Vintthrough the sixth transistor M16(L) and the fifth transistor M15(L).Therefore, the first node N1 may be initialized to the voltage of theinitialization power supply Vint.

When a second scan signal is supplied to the second scan line S2 i, thethird transistor M13(O) may be turned on. The data line Dm may beelectrically connected to the second node N2 when the third transistorM13(O) is turned on.

Subsequently, the light emission control signal may be supplied to thelight emission control line Ei to at least partially overlap the firstscan signal and the second scan signal, and an inverted light emissioncontrol signal may be supplied to the inverted light emission controlline /Ei.

The sixth transistor M16(L) may be turned off when the light emissioncontrol signal is supplied to the light emission control line Ei. Whenthe sixth transistor M16(L) is turned off, a voltage obtained bysubtracting an absolute value of a threshold voltage of the firsttransistor M11(L) from the first driving power supply ELVDD may beapplied to the first node N1 by the first transistor M11(L) in adiode-connected state.

When the inverted light emission control signal is supplied to theinverted light emission control line /Ei, the fourth transistor M14(O)may be turned off and electrical connection between the second node N2and the initialization power supply Vint may be blocked. Since the thirdtransistor M13(O) maintains a turn-on state, a voltage of a data signalmay be applied to the second node N2.

The storage capacitor Cst may be charged with a voltage corresponding toa voltage difference between the second node N2 and the first node N1.Thus, the storage capacitor Cst may store a voltage corresponding to thedata signal and the threshold voltage of the first transistor M11(L).

After the storage capacitor Cst is charged with a predetermined voltage,supply of the first scan signal to the first scan line S1 i and supplyof the second scan signal to the second scan line S2 i may be stopped.When supply of the first scan signal is stopped, second transistorM12(L) and the fifth transistor M15(L) may be turned off. When supply ofthe second scan signal is stopped, third transistor M13(O) may be turnedoff.

Subsequently, supply of the light emission control signal to the lightemission control line Ei may be stopped, and supply of the invertedlight emission control signal to the inverted light emission controlline /Ei may be stopped. When supply of the light emission controlsignal to the light emission control line Ei is stopped, the sixthtransistor M16(L) may be turned on. When the sixth transistor M16(L) isturned on, first transistor M11(L) may be electrically connected toorganic light emitting diode OLED.

When the supply of the inverted light emission control signal to theinverted light emission control line /Ei is stopped, the voltage of theinitialization power supply Vint may be supplied to the second node N2.The voltage of the initialization power supply Vint may be set to apredetermined voltage in a voltage range of the data signal.

For example, the initialization power supply Vint may be set to avoltage higher than or equal to a black data signal or a voltage lowerthan a data signal having another grayscale level.

When the black data signal is applied to the second node N2, a voltageof the second node N2 may remain the same or be increased by apredetermined voltage when the voltage of the initialization powersupply Vint is supplied. A voltage of the first node N1 may be increasedby a predetermined voltage based on the change in the voltage of thesecond node N2 or remain the same as the previous period. For example,the first node N1 may be maintained at a voltage based on a differencebetween an absolute value of the threshold voltage of the firsttransistor M11(L) and the first driving power supply ELVDD. The firsttransistor M11(L) may maintain a turn-off state.

When a data signal corresponding to another grayscale level, except forblack, is applied to the second node N2, the voltage of the second nodeN2 may be reduced by a predetermined voltage if the voltage of theinitialization power supply Vint is supplied. The voltage of the firstnode N1 may be reduced by a predetermined voltage based on the change ofthe voltage of the second node N2. When the voltage of the first node N1is reduced, the first transistor M11(L) may be turned on. The firsttransistor M11(L) may supply current corresponding to the first node N1to organic light emitting diode OLED.

A falling width of the voltage of the second node N2 may be determinedbased on a data signal. For example, a falling width of the voltage ofthe first node N1 may be determined by the data signal, so that thefirst transistor M11(L) may control the amount of current based on thedata signal.

FIG. 9 illustrates another embodiment of a pixel 140 d which includes apixel circuit 144′ and the organic light emitting diode OLED. Theorganic light emitting diode OLED has an anode electrode coupled to thepixel circuit 144′ and a cathode electrode coupled to the second drivingpower supply ELVSS. The organic light emitting diode OLED may emit lightwith predetermined brightness based on the amount of current suppliedfrom the pixel circuit 144′.

The pixel circuit 144′ may include the first transistor M11(L), a secondtransistor M12(O), the third transistor M13(O), the fourth transistorM14(O), a fifth transistor M15(O), the sixth transistor M16(L) and thestorage capacitor Cst. The pixel circuit 144′ may have substantially thesame configuration as the pixel circuit 144 in FIG. 7, except that thesecond transistor M12(O) and the fifth transistor M15(O) are oxide thinfilm transistors.

The second transistor M12(O) may be coupled between the first node N1and the second electrode of the first transistor M11(L). A gateelectrode of the second transistor M12(O) may be connected to the ithsecond scan line S2 i. The second transistor M12(O) may be turned onwhen the second scan signal is supplied to the ith second scan line S2i. When the second transistor M12(O) is turned on, the first transistorM11(L) may be placed in a diode-connected state. The second transistorM12(O) may be, for example, an n-type oxide thin film transistor.

When the second transistor M12(O) is an oxide thin film transistor,leakage current flowing from the first node N1 to the second electrodeof the first transistor M11(L) may be reduced and the organic lightemitting diode OLED may emit light with desired brightness.

The fifth transistor M15(O) may be connected between the anode electrodeof the organic light emitting diode OLED and the initialization powersupply Vint. A gate electrode of the fifth transistor M15(O) may becoupled to the ith second scan line S2 i. The fifth transistor M15(O)may be turned on when a second scan signal is supplied to the ith secondscan line S2 i. When the fifth transistor M15(O) is turned on, a voltageof the initialization power supply Vint may be supplied to the anodeelectrode of the organic light emitting diode OLED. The fifth transistorM15(O) may be, for example, an n-type oxide thin film transistor.

When the fifth transistor M15(O) is an oxide thin film transistor,leakage current flowing from the anode electrode of the organic lightemitting diode OLED to the initialization power supply Vint may bereduced and the organic light emitting diode OLED may emit light withdesired brightness. In addition, when the second transistor M12(O) andthe fifth transistor M15(O) are n-type transistors, the first scan lineS1 may be removed. The pixel 140 d may be driven by a second scan lineS2.

FIG. 10 illustrates an embodiment of a method for driving the pixel inFIG. 9. The method includes, first, supplying a second scan signal tothe second scan line S2 i. When the second scan signal is supplied tothe second scan line S2 i, the second transistor M12(O), the thirdtransistor M13(O) and the fifth transistor M15(O) may be turned on.

When the fifth transistor M15(O) is turned on, a voltage of theinitialization power supply Vint may be supplied to the anode electrodeof the organic light emitting diode OLED. When a voltage of theinitialization power supply Vint is supplied to the anode electrode ofthe organic light emitting diode OLED, the organic capacitor Coled maybe discharged.

When the second transistor M12(O) is turned on, the first transistorM11(L) may be placed in a diode-connected state. The first node N1 maybe electrically connected to the initialization power supply Vintthrough the sixth transistor M16(L) and the fifth transistor M15(O).Therefore, the first node N1 may be initialized to the voltage of theinitialization power supply Vint.

When the third transistor M13(O) is turned on, the data line Dm may beelectrically connected to the second node N2.

Subsequently, to partially overlap a period of the second scan signal, alight emission control signal may be supplied to the light emissioncontrol line Ei and an inverted light emission control signal may besupplied to the inverted light emission control line /Ei. When the lightemission control signal is supplied to the light emission control lineEi, the sixth transistor M16(L) may be turned off. When the sixthtransistor M16(L) is turned off, a voltage, based on a differencebetween an absolute value of a threshold voltage of the first transistorM11(L) and first driving power supply ELVDD, is applied to the firstnode N1 by the first transistor M11(L) in a diode-connected state.

When the inverted light emission control signal is supplied to theinverted light emission control line /Ei, the fourth transistor M14(O)may be turned off. When the fourth transistor M14(O) is turned off,electrical connection between the second node N2 and initializationpower supply Vint may be blocked. Since the third transistor M13(O)maintains a turn-on state, a voltage of a data signal may be applied tosecond node N2.

The storage capacitor Cst may store a voltage based on a differencebetween the second node N2 and the first node N1. For example, a voltagecorresponding to the data signal and the threshold voltage of the firsttransistor M11(L) may be stored in the storage capacitor Cst.

After a predetermined voltage is stored in the storage capacitor Cst,supply of the second scan signal to the second scan line S2 i may bestopped. When the supply of the second scan signal to the second scanline S2 i is stopped, the second transistor M12(O), the third transistorM13(O) and the fifth transistor M15(O) may be turned off.

Subsequently, supply of the light emission control signal to the lightemission control line Ei may be stopped and supply of the inverted lightemission control signal to the inverted light emission control line /Eimay be stopped. The sixth transistor M16(L) may be turned on when supplyof the light emission control signal to the light emission control lineEi is stopped. When the sixth transistor M16(L) is turned on, the firsttransistor M1(L) may be electrically connected to the organic lightemitting diode OLED. When supply of the inverted light emission controlsignal to the inverted light emission control line /Ei is stopped, thevoltage of the initialization power supply Vint may be supplied to thesecond node N2.

A voltage of the first node N1 may be changed based on the change involtage of the second node N2. The first transistor M11(L) may controlthe amount of current flowing from the first driving power supply ELVDD,through the organic light emitting diode OLED, and to the second drivingpower supply ELVSS based on the voltage of the first node N1. In oneembodiment, the scan driver 110 may include a plurality of stagecircuits for generating at least one of a first scan signal, a secondscan signal or a light emission control signal.

FIG. 11 illustrates an embodiment of a stage circuit which includes anoxide semiconductor thin film transistor and a Low TemperaturePoly-Silicon (LTPS) thin film transistor. The stage circuit may includea first transistor T1(L), a second transistor T2(L), a fifth transistorT5(L), a sixth transistor T6(L) and a ninth transistor T9(L) which arecomposed of LTPS thin film transistors. In addition, the stage circuitmay include a third transistor T3(O), a fourth transistor T4(O), aseventh transistor T7(O), an eighth transistor T8(O) and a tenthtransistor T10(O) which are composed of oxide semiconductor thin filmtransistors.

The first transistor T1(L), the second transistor T2(L), the thirdtransistor T3(O), and the fourth transistor T4(O) may be coupled inseries between a first power supply VDD and a second power supply VSS.The first power supply VDD may be set to a high voltage and the secondpower supply VSS may be set to a low voltage.

A gate electrode of the first transistor T1(L) may receive a start pulseFLM or an output signal from the previous stage. The first transistorT1(L) may be, for example, a p-type transistor which turns on when thestart pulse FLM or the output signal (high voltage) from the previousstage is not supplied.

A gate electrode of the second transistor T2(L) may receive a firstclock signal CLK1. The second transistor T2(L) may be, for example, ap-type transistor which is turned on when the first clock signal CLK1 isset to a low voltage.

A gate electrode of the third transistor T3(O) may receive a secondclock signal CLK2. The third transistor T3(O) may be, for example, ann-type transistor and turned on when the second clock signal CLK2 is setto a high voltage. The first clock signal CLK1 and the second clocksignal CLK2 may have the same cycle and be set to phase invertedsignals.

A gate electrode of the fourth transistor T4(O) may receive the startpulse FLM or an output signal from the previous stage. The fourthtransistor T4(O) may be, for example, an n-type transistor and turned onwhen the start pulse FLM or the output signal from the previous stage issupplied. In addition, a common node between the second transistor T2(L)and the third transistor T3(O) may be electrically connected to thefirst node N1.

The fifth transistor T5(L), the sixth transistor T6(L), the seventhtransistor T7(O), and the eighth transistor T8(O) may be coupled inseries between the first power supply VDD and the second power supplyVSS.

A gate electrode of the fifth transistor T5(L) may be electricallyconnected to an output terminal. The fifth transistor T5(L) may be, forexample, a p-type transistor and turned on or off based on a voltagefrom the output terminal.

A gate electrode of the sixth transistor T6(L) may receive the secondclock signal CLK2. The sixth transistor T6(L) may be, for example, ap-type transistor and turned on when the second clock signal CLK2 is setto a low voltage.

A gate electrode of the seventh transistor T7(O) may receive the firstclock signal CLK1. The seventh transistor T7(O) may be, for example, ann-type transistor and turned on when the first clock signal CLK1 is setto a high voltage.

A gate electrode of the eighth transistor T8(O) may be electricallyconnected to the output terminal. The eighth transistor T8(O) may be,for example, an n-type transistor and turn on or off based on a voltageof the output terminal. In addition, a common node between the sixthtransistor T6(L) and the seventh transistor T7(O) may be electricallyconnected to the first node N1.

The ninth transistor T9(L) and the tenth transistor T10(O) may becoupled in series between the first power supply VDD and the secondpower supply VSS.

A gate electrode of the ninth transistor T9(L) may be coupled to thefirst node N1. The ninth transistor T9(L) may be, for example, a p-typetransistor and turned on or off based on a voltage of the first node N1.

A gate electrode of the tenth transistor T10(O) may be connected to thefirst node N1. The tenth transistor T10(O) may be, for example, ann-type transistor and turned on or off based on the voltage of the firstnode N1. In addition, a common node between the ninth transistor T9(L)and the tenth transistor T10(O) may be electrically connected to theoutput terminal.

Thus, in one embodiment, the stage circuit includes one or more p-typetransistors and one or more n-type transistors. In one embodiment, thestage circuit may include one or more LTPS thin film transistors asp-type transistors and one or more oxide semiconductor thin filmtransistors as n-type transistors. When the stage circuit is formedusing LTPS thin film and oxide semiconductor thin film transistors,leakage current may be reduced and a high driving speed may be ensured.

The methods, processes, and/or operations described herein may beperformed by code or instructions to be executed by a computer,processor, controller, or other signal processing device. The computer,processor, controller, or other signal processing device may be thosedescribed herein or one in addition to the elements described herein.Because the algorithms that form the basis of the methods (or operationsof the computer, processor, controller, or other signal processingdevice) are described in detail, the code or instructions forimplementing the operations of the method embodiments may transform thecomputer, processor, controller, or other signal processing device intoa special-purpose processor for performing the methods herein.

The drivers, controllers, and other processing features described hereinmay be implemented in logic which, for example, may include hardware,software, or both. When implemented at least partially in hardware, thedrivers, controllers, and other processing features may be, for example,any one of a variety of integrated circuits including but not limited toan application-specific integrated circuit, a field-programmable gatearray, a combination of logic gates, a system-on-chip, a microprocessor,or another type of processing or control circuit.

When implemented in at least partially in software, the drivers,controllers, and other processing features may include, for example, amemory or other storage device for storing code or instructions to beexecuted, for example, by a computer, processor, microprocessor,controller, or other signal processing device. The computer, processor,microprocessor, controller, or other signal processing device may bethose described herein or one in addition to the elements describedherein. Because the algorithms that form the basis of the methods (oroperations of the computer, processor, microprocessor, controller, orother signal processing device) are described in detail, the code orinstructions for implementing the operations of the method embodimentsmay transform the computer, processor, controller, or other signalprocessing device into a special-purpose processor for performing themethods described herein.

In accordance with one or more of the aforementioned embodiments, apixel may include at least one oxide semiconductor thin film transistorand at least one LTPS thin film transistor. The oxide semiconductor thinfilm transistor having excellent off characteristics may be in a currentleakage path, in order to reduce current leakage and display an imagewith desired brightness.

In addition, an LTPS thin film transistor having excellent drivingcharacteristics may be in a current supply path for supplying current toan organic light emitting diode, so that current may be stably suppliedto the organic light emitting diode by high driving characteristics ofthe LTPS thin film transistor. In addition, a stage circuit may includean oxide semiconductor thin film transistor and an LTPS thin filmtransistor, so that the stage circuit may have reduced current leakageand have a high driving speed.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. Theembodiments (or portions thereof) may be combined to form additionalembodiments. In some instances, as would be apparent to one of ordinaryskill in the art as of the filing of the present application, features,characteristics, and/or elements described in connection with aparticular embodiment may be used singly or in combination withfeatures, characteristics, and/or elements described in connection withother embodiments unless otherwise indicated.

Accordingly, it will be understood by those of skill in the art thatvarious changes in form and details may be made without departing fromthe spirit and scope of the embodiments set forth in the claims.

What is claimed is:
 1. A pixel, comprising: an organic light emittingdiode; a first transistor having a first electrode coupled to a firstnode and a second electrode coupled to an anode electrode of the organiclight emitting diode, the first transistor to control an amount ofdriving current flowing from a first driving power supply coupled to thefirst node to a second driving power supply through the organic lightemitting diode; a second transistor coupled between a data line and thefirst node, the second transistor to turn on when a first scan signal issupplied to a first scan line; a third transistor coupled between a gateelectrode and the second electrode of the first transistor, the thirdtransistor to turn on when a second scan signal is supplied to a secondscan line; and a fourth transistor coupled between the gate electrode ofthe first transistor and an initialization power supply, the fourthtransistor to turn on when a third scan signal is supplied to a thirdscan line, wherein the first transistor is a Low TemperaturePoly-Silicon (LTPS) thin film transistor and the third transistor andthe fourth transistor are oxide semiconductor thin film transistors,wherein each of the third transistor and the fourth transistor includesan active layer including an oxide semiconductor material.
 2. The pixelas claimed in claim 1, wherein the second transistor is a p-type LTPSthin film transistor.
 3. The pixel as claimed in claim 1, wherein thesecond transistor is an n-type oxide semiconductor thin film transistor.4. The pixel as claimed in claim 3, wherein: the first scan signal andthe second scan signal are a same scan signal, and the first scan lineand the second scan line are a same scan line.
 5. The pixel as claimedin claim 1, further comprising: a fifth transistor coupled between theinitialization power supply and the anode electrode of the organic lightemitting diode, the fifth transistor to turn on when the first scansignal is supplied to the first scan line, wherein the fifth transistoris a p-type LTPS thin film transistor.
 6. The pixel as claimed in claim1, further comprising: a fifth transistor coupled between theinitialization power supply and the anode electrode of the organic lightemitting diode, the fifth transistor is to turn on when the second scansignal is supplied to the second scan line, wherein the fifth transistoris an n-type oxide semiconductor thin film transistor.
 7. The pixel asclaimed in claim 1, further comprising: a sixth transistor coupledbetween the second electrode of the first transistor and the anodeelectrode of the organic light emitting diode, the sixth transistor isto turn off when a light emission control signal is supplied to a lightemission control line; and a seventh transistor coupled between thefirst node and the first driving power supply, the seventh transistor isto turn off when the light emission control signal is supplied, whereinthe sixth transistor and the seventh transistor are p-type LTPS thinfilm transistors.
 8. The pixel as claimed in claim 1, wherein: alltransistors directly connected to the gate electrode of the firsttransistor are oxide semiconductor thin film transistors, and alltransistors coupled to the first transistor and through which thedriving current flows are LTPS thin film transistors.
 9. A pixel,comprising: an organic light emitting diode; a first transistor tocontrol an amount of driving current flowing from a first driving powersupply coupled to a first electrode, through the organic light emittingdiode, and to a second driving power supply based on a voltage of afirst node; a second transistor coupled between the first node and asecond electrode of the first transistor, the second transistor is toturn on when a first scan signal is supplied to a first scan line; astorage capacitor coupled between the first node and a second node; athird transistor coupled between a data line and the second node, thethird transistor to turn on when a second scan signal is supplied to asecond scan line; and a fourth transistor coupled between the secondnode and an initialization power supply, the fourth transistor to turnoff when an inverted light emission control signal is supplied to aninverted light emission control line, wherein the first transistor is ap-type LTPS thin film transistor and the third transistor and the fourthtransistor are n-type oxide semiconductor thin film transistor, wherein:all transistors directly connected to a gate electrode of the firsttransistor are oxide semiconductor thin film transistors, and alltransistors coupled to the first transistor and through which thedriving current flows are LTPS thin film transistors.
 10. The pixel asclaimed in claim 9, wherein the second transistor is a p-type LIPS thinfilm transistor.
 11. The pixel as claimed in claim 9, wherein the secondtransistor is an n-type oxide semiconductor thin film transistor. 12.The pixel as claimed in claim 11, wherein the first scan line and thesecond scan line are a same scan line.
 13. The pixel as claimed in claim9, further comprising: a fifth transistor coupled between theinitialization power supply and an anode electrode of the organic lightemitting diode, the fifth transistor to turn on when the first scansignal is supplied to the first scan line, wherein the fifth transistoris a p-type LTPS thin film transistor.
 14. The pixel as claimed in claim9, further comprising: a fifth transistor coupled between theinitialization power supply and an anode electrode of the organic lightemitting diode, the fifth transistor to turn on when the second scansignal is supplied to the second scan line, wherein the fifth transistoris an n-type oxide semiconductor thin film transistor.
 15. The pixel asclaimed in claim 9, further comprising: a sixth transistor coupledbetween the second electrode of the first transistor and an anodeelectrode of the organic light emitting diode, the sixth transistor toturn off when a light emission control signal is supplied to a lightemission control line, wherein the sixth transistor is a p-type LTPSthin film transistor and the light emission control signal and theinverted light emission control signal are inverted relative to eachother.
 16. An organic light emitting display device, comprising: pixelsconnected to scan lines, light emission control lines, and data lines; ascan driver to drive the scan lines and the light emission controllines; and a data driver to drive the data lines, wherein at least onepixel in a horizontal line, among the pixels, includes: an organic lightemitting diode; a first transistor having a first electrode coupled to afirst node and a second electrode coupled to an anode electrode of theorganic light emitting diode, wherein the first transistor is to controlan amount of driving current flowing from a first driving power supplycoupled to the first node, through the organic light emitting diode, andto a second driving power supply; a second transistor coupled between adata line and the first node, the second transistor to turn on when afirst scan signal is supplied to a first scan line; a third transistorcoupled between a gate electrode and the second electrode of the firsttransistor, the third transistor to turn on when a second scan signal issupplied to a second scan line; and a fourth transistor coupled betweenthe gate electrode of the first transistor and an initialization powersupply, the fourth transistor to turn on when a third scan signal issupplied to a third scan line, wherein the first transistor is a LowTemperature Poly-Silicon (LTPS) thin film transistor and the thirdtransistor and the fourth transistor are oxide semiconductor thin filmtransistors, wherein all transistors directly connected to the gateelectrode of the first transistor are oxide semiconductor thin filmtransistors, and all transistors coupled to the first transistor andthrough which the driving current flows are LTPS thin film transistors.17. The organic light emitting display device as claimed in claim 16,wherein the at least one pixel includes a fifth transistor coupledbetween the initialization power supply and the anode electrode of theorganic light emitting diode, the fifth transistor to turn on when thesecond scan signal is supplied to the second scan line, wherein thefifth transistor is an n-type oxide semiconductor thin film transistor.18. The organic light emitting display device as claimed in claim 16,wherein the at least one pixel includes: a sixth transistor coupledbetween the second electrode of the first transistor and the anodeelectrode of the organic light emitting diode, the sixth transistor toturn off when a light emission control signal is supplied to a lightemission control line; and a seventh transistor coupled between thefirst node and the first driving power supply, the seventh transistor toturn off when the light emission control signal is supplied, wherein thesixth transistor and the seventh transistor are p-type LTPS thin filmtransistors.
 19. The organic light emitting display device as claimed inclaim 16, wherein: the scan driver includes a plurality of stagecircuits to drive the scan lines and the light emission control lines,and at least one of the stage circuits includes: an eleventh transistor,a twelfth transistor, a thirteenth transistor, and a fourteenthtransistor coupled in series between a first power supply and a secondpower supply set to a voltage lower than the first power supply; afifteenth transistor, a sixteenth transistor, a seventeenth transistorand an eighteenth transistor coupled in series between the first powersupply and the second power supply; and a nineteenth transistor and atwentieth transistor coupled in series between the first power supplyand the second power supply, wherein the eleventh transistor is a p-typeLTPS thin film transistor and has a gate electrode to receive an outputsignal from a previous stage or a start pulse, the twelfth transistor isset to a p type LTPS thin film transistor and has a gate electrode toreceive a first clock signal, the thirteenth transistor is an n-typeoxide semiconductor thin film transistor and has a gate electrode toreceive a second clock signal having a same cycle as the first clocksignal and an inverted phase, the fourteenth transistor is an n-typeoxide semiconductor thin film transistor and has a gate electrode toreceive the output signal from the previous stage or the start pulse,the fifteenth transistor is set to a p type LTPS thin film transistorand has a gate electrode coupled to an output terminal, the sixteenthtransistor is a p-type LTPS thin film transistor and has a gateelectrode to receive the second clock signal, the seventeenth transistoris an n-type oxide semiconductor thin film transistor and has a gateelectrode to receive the first clock signal, the eighteenth transistoris an n type oxide semiconductor thin film transistor and has a gateelectrode coupled to the output terminal; the nineteenth transistor is ap-type LTPS thin film transistor and has a gate electrode coupled to thefirst node, the twentieth transistor is an n-type oxide semiconductorthin film transistor and has a gate electrode coupled to the first node,and a first common node between the twelfth transistor and thethirteenth transistor and a second common node between the sixteenthtransistor and the seventeenth transistor are electrically connected tothe first node.